Conventional oxide-isolated, unguarded Schottky barrier diodes fabricated on a silicon substrate include a body of a silicide of a near-noble metal (palladium, platinum or nickel) in intimate contact with the substrate. Diode operation relies on the potential barrier established at the interface between the substrate and the silicide body. By way of example, a conventional unguarded Schottky barrier diode has the structure illustrated in FIG. 1, and comprises a wafer 2 of n-type silicon having a surface layer 4 of SiO.sub.2 defining an opening in which a body 6 of Pd.sub.2 Si is disposed. Layer 4 and the body 6 are covered by a layer 8 of refractory diffusion barrier metal such as TiW.
It has been found that diodes of this form have very inconsistent properties, varying widely from device to device on the same wafer. Typically, the diode quality factor n varies between 1.1 and 3 (one being ideal), depending on the device size, processing history and geometrical profile. The forward voltage characteristics of the diode also vary widely. Accordingly, good matching of two or more diodes is very difficult to obtain. In addition, reverse characteristics of the conventional diodes (breakdown voltage and current leakage) are far from ideal. Device properties are further degraded by treatment at elevated temperatures (400 deg. C.).
It is believed that a primary reason for the poor properties of the conventional unguarded Schottky barrier diode shown in FIG. 1 is that a parasitic Ti silicide/Si oxide/silicon MIS diode is formed around the perimeter of the body 6. Due to the large differences in heats of formation for titanium silicide and titanium oxide as compared with silicon dioxide, the titanium in the layer 8 extracts silicon from the surface region of the layer 4, so that the silicon dioxide in the surface region, and particularly around the perimeter of the body 6, is reduced and quantum-mechanical tunneling occurs in the resulting region. This perimeter region is typically 50 to 500 A wide, depending on the profile of the cut formed in the layer 4 in order to expose the wafer 2. This effect is aggravated by the fact that titanium is a low work function metal, and accordingly causes an accumulation of electrons at the surface of the n-type silicon. Accordingly, the parasitic MIS diode has a very low barrier and is leaky.